code: def _m(a, b, c, d=None):
      """return Matrix([[a, b], [c, d]]) from matrices
      in Matrix or list form.
  
      Examples
      ========
  
      >>> from sympy import Matrix
      >>> from sympy.solvers.simplex import _abcd, _m
      >>> m = Matrix(3, 3, range(9))
      >>> L = _abcd(m, list=True); L
      ([[0, 1], [3, 4]], [2, 5], [[6, 7]], [8])
      >>> _abcd(m)
      (Matrix([
      [0, 1],
      [3, 4]]), Matrix([
      [2],
      [5]]), Matrix([[6, 7]]), Matrix([[8]]))
      >>> assert m == _m(*L) == _m(*_)
      """
      a, b, c, d = [Matrix(i) for i in (a, b, c, d or [0])]
      return Matrix([[a, b], [c, d]])
  
imports: from sympy.core import sympify
  from sympy.core.exprtools import factor_terms
  from sympy.core.relational import Le, Ge, Eq
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy
  from sympy.core.sorting import ordered
  from sympy.functions.elementary.complexes import sign
  from sympy.matrices.dense import Matrix, zeros
  from sympy.solvers.solveset import linear_eq_to_matrix
  from sympy.utilities.iterables import numbered_symbols
  from sympy.utilities.misc import filldedent
label_desc: Use image node_id 5 for calling a global function with example usage: _m(a, b, c, d) and returns: Matrix